Oh my, I'm so sorry, I didn't see your post earlier.
Yes, I do believe that this might be just a phase. My DD is no 2 1/2 and consistently able to self-settle. Has been doing so for close to a year. BUT, we have had a few periods of regression. I have always just rolled with it. Sometimes we lay down with her until she was asleep.
You could consider moving him into a single bed with guard rail, so you can lie down with him. Once he feels safe in his new bed you can start leaving before he is fully asleep. Whenever DD asked for me to stay, i would promise her that I'd be jsut outside and that I will be back in a minute (after having a drink for example). I think me coming and going re-assured her that I'm still around, evben if she can't see me.
it is a slow process. But I think it is worth it.
Good luck!