most T's I've called by their first names, usually because that is how they introduce themselves.
One T had a PsyD. A tthe beginning, I referred to her by her title and last name. As time went on and things became more formal, I called her by her title and first name or first initial. I could have asked her how she prefers to be addressed, but I was too shy, as if I should have figured that out on my own. She never corrected anything. She changed what she addressed herself wiht the level of formality required for the interaction (in communicating with other professionals, she used her full titile and name, when leaving messages, she would use her title & cirst name or initial, or drop the title and use her first name. In recent text communications, she just used her initials).
If it feels too formal, I don't feel a connection or much trust. Even with my PCP, we often refer to eachother by nicknames.
When talking to friends or family about my therapist, I use first names to identify them.