Perhaps you can set designated times that you will check your phone and reply. E.g 8:30am, 12:30 pm and 5:30pm. Allow a max of 10 minutes per time. Ie 30 mins per day. Just a suggestion.
if you can answer the messages on your computer, do that. if not, try to place your phone in a place that makes it difficult for you to settle down and relax. instead of placing my charger next to my bed, i place it across the room that way when a notification happens to come through i won’t want to get out of bed to check my phone. also, you can remind yourself that you are trying to not use your phone as often. and if you do go back to using your phone that’s okay, just remember to give yourself the space to try again.