I don’t know why that should suddenly have happened but a couple of things to check:

Is your 2.4GHz router band set to use protocols b/g/n, and not just n?

Is your phone connecting to the 2.4GHz or 5GHz band?  (With some routers being on 5GHz can be problematic).

Do you have any other controller devices?

Thanks, John. Nothing really has changed. Same wifi and router network for 1.5 years. I am not too techie so I try not to mess with things too much. What is strange now. is I logged into my Sonos app on my MacBook air just now and I see the system with no cable connected to a device but only 6 of my 7 speakers are seen that I can group. I just looked to see if my iPhone Sonos app was now working and it says “Unable to connect to Sonos “ and when I click on join a nearby Sonos system on the iPhone app, it says We cvan’t find a Sonos systems...yet is is playing right now a few feet from me. I have a Beam, a bunch of Play 1’s and Play 3’s all on OS S2. Thanks!

Also not quite sure what this means “Is your 2.4GHz router band set to use protocols b/g/n, and not just n?” Where would I check this, please? 

I see the blue light on for the 2.4 and 5 on my wifi unit. 

Something else I jus remembered. If it is an iPhone then the following recently started to apply

"Local network access is required for your Sonos app to set up or connect with your Sonos products on your network.".

I must admit that I would not have expected that to be related to whether wired or not,  but worth checking.

Also, if your phone is connecting to your 5GHz router band that might explain the problem.