assistive access and texting

I'm trying to figure out if assistive access will work for my father. He has a few different neuro issues going on but the main issue is his vision. He can see but his brain doesn't necessarily process what his eyes see correctly. He depends a lot on texting to keep in communication with friends and family and he can send texts by using Siri pretty easily. But is there a way for the texts to be read out loud? Anyone have any suggestions? I've looked into some other options but can't seem to find what I'm looking for. He's used to his iPhone and if we can we'd like to stick with it.