Not supported yet. If you're going straight to social media from your phone, do the captions there. If you're going to edit the final on the desktop, wait to do the captions. The animations available in the mobile app are very basic, but it's a start.
On the iPhone, once you export there is message with Learn More. That link takes you to that web page. The features work in the mobile app; they don't transfer to the desktop.
The box says:
Certain features are not currently supported when transferring projects to Premiere on desktop:
Text
Text animations
Captions
Caption animations
Audio
Enhance speech
Color
Lighroom Looks
Color Adjustments
Effects
Remove background
Text and clip animations
Flip
Photo motion
Noir background