1. We would say "look at you phone." 2. We would avoid the word "workday" and say "have a nice day at work" or something like that. 3. We would say "on the phone."

1. 'Look at your phone' refers to the physical object. 'Look at [something] ' means take your eyes off one thing and turn them towards something else. You look at your phone in the same way as you look at a picture or look at a magazine or look at a menu. 'Look at' is a standard combination of verb and preposition. 3. 'Talk on the phone' refers to the technology. We often use 'on' to refer to media and means of communication - on TV, on the radio, on the internet, on Skype.