You’re going to be challenged. Your PLAYBAR has neither the AirPlay 2 or Bluetooth electronics necessary to connect to your iPhone. You’d need a newer Sonos speaker, which you could send the sound to, and group your PLAYBAR with. 

Is there a reason other than an app glitch that doesn’t allow me to play my iPhones music library via the Sonos app?

Apple has disallowed it. As has Google on Android. Unfortunately, music stored on ‘mobile devices’ can not be played by external devices, such as Sonos, you must use a ‘player’ on the device, and ‘cast’ to the Sonos. 

Not trying to argue here but if Apple disallowed playing stored music on external devices why can I play my library on any Bluetooth/airplay speaker? I also have a couple Bose soundtouch devices and I can play my library through the soundtouch app, not just BT/airplay. 

Also wouldn’t explain why about 1/3 of the songs from my library will play.

Furthermore why would sonos bother having the app show me a bunch of greyed out songs from an internal library that it’s disallowed from playing. 

I appreciate your responses but I don’t think your logic/answer is correct. 

Here’s an example- one album from my CD collection. This one plays most tracks but for some reason there are 2 which don’t. Same CD, same rip, same formatting. 
 

Using Bluetooth or AirPlay 2, you’re using a ‘player’ on your iPhone and ‘casting’ the sound to the Sonos. When using the Sonos controller, your using the app to tell the Sonos device to reach out where the music is stored to get and play the music. 

Apple and Google have both changed their OS (if you’re current) to not allow an external device (like the Sonos system) to use their mobile device’s data storage as a source. And apparently Sonos subsequently was told to remove that ability. I’d imagine there might have been threats to delist their software in the various stores, but I don’t work for Sonos, so I’m guessing. 

My guess in your case is some of this music you’re playing is stored on Apple’s servers, and not just locally, and the Sonos is grabbing the data from there to play it, and not from your phone, but you’d likely need to confirm that by calling Sonos Support directly to discuss it.

Sounds to me like it’s easier for Sonos to blame Apple for an issue than fix it. 
 

If it’s selecting only music Apple has on its servers I assure you they have the entire AC/DC catalogue. Apple Music isn’t missing the title track for that album I posted as an example.
 

Again this process works fine via the Bose soundtouch app. WITHOUT using airplay or Bluetooth. 

Because, I believe, the BOSE app is ‘playing’ on the device, and ‘casting’ the result to the speakers, which isn’t the way some others handle it, like Sonos.

But feel free to be angry about it. I’m convinced Sonos wasn’t overly happy about being forced to make that change, and I suspect other companies weren’t overly excited about it either. 

Many have blamed Sonos, but they would be wrong.  At least Sonos actually tried to work with Apple for over a year to fix this, others like Bluesound just got rid of it once it started deteriorating due to Apple’s new rules.  You can read the whole saga that went down at the time here:

As far as the Bose Soundtouch is concerned, it hasn’t been sold in 5 years and their playing of local libraries was plagued with the same problems as Sonos.  The Soundtouch line was discontinued before Apple made the final changes that caused Sonos to remove this function completely. 

I’m angry at all. I’m just pointing out the holes in your explanation. Like why some songs works and some don’t. As the example in the AC/DC album it’s not an Apple Music streaming catalogue gap, resulting in the sonos being able to stream only part of the album. Apple isn’t missing the title track. So by the explanation the entire album would be playable with no tracks being greyed out. 
 

It’s also not a local file format difference or DRM issue as that album was ripped to my local library from the same disc at the same time.

It may be “old” tech and the app it’s perfect like not showing album art. But it plays my local library off my phone flawlessly and the volume control it much more responsive than the sonos app. I use it daily. 

I really don’t know what you are trying to do.  Playing songs located on your mobile device is not even partially supported, it simply no longer exists as of 2020.  Whatever AC/DC tracks you are seeing (or partially seeing) in the Sonos app, they aren’t the ones stored on your device (which used to be in their own “On this iDevice” section of the app).  I repeat, no tracks located on your mobile device can be played (or even seen) in the Sonos app.  

So in that screenshot of the Sonos app you attached above, those cannot possibly be tracks located on your phone.  They are from some service or a local library stored on a PC or NAS. 

I did a little investigating.  That version of “Ain’t No Fun (Waiting Round to Be a Millionaire)” is marked with an E for Explicit.  I didn’t test it myself, but I imagine if your Apple Music account is set to not allow explicit lyrics, it will be greyed out.  

When I launch sonos and select Apple Music as my service it pulls up a window that looks like the native Apple Music app down to the selections available are the same (albums, artists, songs, playlists). 

 

When I nagivate that way to my AC/DC albums Dirty Deeds is missing 2 tracks. Other albums such as back in black are not. This example is purely because of alphabetical order and was the first artist I picked.
 

  
However when I select search it allows to search Apple Music or your library. Pardon me for being mislead but “your library” gives the impression it’s going to search what’s on my phone in my native library, not a streaming service. Especially since the other option is clearly searching the streaming service. 
 

If I search “your library” for the same album I get the same result as if I navigated there from my list of albums on the initial option screen (albums, artists, etc).

However if I search Apple Music for the same album I get the entire track list with nothing greyed out.

I acknowledge I’m not an app expert or developer. But this makes no sense to me and points to an app glitch on the sonos side, not an Apple issue. That or the layout and language used such as “your library” don’t mean what they do on every other app I have. 
 

While searching each time for a title to listen too is a bit of a nuisance it’s more of an issue with my playlists since most of them are missing 1/3 to ½ of the tracks due to being greyed out. 

“Your library” is not the music on your phone.  It is the music you own in iTunes duplicated in Apple Music’s cloud.  So that is coming from Apple Music, not the your phone. The tracks must be missing from there, because nothing in the Sonos app can access any music files on your phone.  Somehow you need to sync your iTunes library (or whatever it uses now) with your Apple Music account.