Posting this from my phone but yeah, deaf people use phones all the time. We qualify for discounted data-only rates with no or limited voice minutes from the major carriers. That used to be an awesome deal back then but not really nowadays.
There are video relay apps so you can make calls and receive them! It's a different number from your device number for texting though. Glide is the new hotness right now, it's an app that's like texting but with videos instead.
Phones are not a new thing for deaf people either. Instead of Nokias or Razrs, we had those little pagers with email address then moved onto Sidekicks which was the greatest phone ever. It also had the first data-only plan and it was super popular with deafies until Danger went out of business. RIP Danger

After that, people just started using regular smartphones.
Like what you said, we use them for everything except calling but there are some deaf people who are able to make calls too either unassisted or using something like captel which is a half text relay service as it only relays the caller in with the audio too and allows the deaf person to speak using their own voice.