Probably the most popular telephone captioning app for smartphone calls is InnoCaption.
https://innocaption.com

InnoCaption requires an additional telephone number. You can use your regular cellphone number by having your calls forward to your InnoCaption telephone number. 

To use the service you don't have to type anything.

InnoCaption now has a computer option.

Captioning apps for conversations
There are a variety of captioning app options to use for conversations. Of the available options, Ava is the only one that you can maintain social distancing.  It is available for smartphones, computers, online and offline.
https://www.ava.me

We all have our own preferences. You need to experiment with them to determine which one you like the best.