Internet History

I understand my employer can track my internet usage on their network. however can they track my phone history of what i viewed when i was away from work (not on their network)? What if i never deleted the history of what I was searching and came to work but never accessed the internet from my iPhone (safari was closed) again this was accessed from a different network. Thanks! and keep your minds out of the gutter hahaha it was nothing like you're thinking!