I’m dry on the phone and I hate it

I (19M) call my American girlfriend (22F) long-distance. However, I’m autistic and very nervous when I call.

I tend to be very dry and only say one word or one thing, and I don’t know how to properly respond when my girlfriend gets anxiety attacks over call and she has to leave from being overstimulated.

I just say “oh okay” because I don’t know what to say.