controlling speakers

Yes, you can have multiple devices with the app installed which can all control the system.

Remember Sonos only works with one account, so you'd log in to the app on both phones wirth the same credentials. You can add multiple music servce account to Sonos, making different account the preferred account on tdifferent phones: Use multiple accounts for the same content service | Sonos

You can use up to 31 phones if you like (total device limit=32)

Sonos have previously stated:

There is no set limit for Sonos Controllers in one HouseHold, except to say this: "You can have up to 32 controllers controlling 1 Player or 1 controller controlling up to 32 Players."