Every T has different feelings around contact outside of sessions. My first two T's did not encourage it, and the only way to contact them was via their office phone number. I did not feel at all welcome to contact them for anything other than scheduling changes.

My current T strongly encourages me to reach out to her, via email or phone. Both methods of contact were her suggestions to me. It didn't occur to me that I could reach out between sessions until she asked me to do so. I try to respect her time, and only call if it's urgent. I tend to email no more than once a week, but it's usually just me processing things, and doesn't require an indepth response from my T. I only increase my contact when my T asks me to (when I was really struggling, she asked for a daily check in email).