Hi Sandy,
Our 2007 Phoenix Cruiser 2350 does not have a sofa, but rather a dinette so I have no first-hand knowledge. With one exception, I understand every sofa Phoenix installed over the years, do NOT officially offer storage. It does not mean you can't tuck something under there. It's just not designed to store stuff.
Sometime around 2010-2012, Phoenix replaced the old style jack-knife sofa with a more comfortable sofa bed which included a nice wide drawer underneath. The bed used a blow-up air mattress. It was all the rage with new owners, but the love affair didn't seem to last, primarily concerning the longevity and inconvenience of the air mattress.
In the years that followed, Phoenix replaced the air bed sofa with a very comfortable duel recliner sofa that opens flat for sleeping. Various flavors of that concept continue to this day with never a complaint from PC owners. Hopefully someone with that type of sofa will comment regarding possible storage.
If sofa bench storage is a very high priority for you, you could maximize storage through something home made. But it likely won't be as comfortable to sit on, and converting it into a bed could present even more challenges.
Ron Dittmer