Back up your contacts to the cloud or a SIM card before you ditch the smartphone. Do this first. You cannot afford to lose critical numbers, and recovering them later is a nightmare.
Download offline maps and save essential info while you still have Wi-Fi. Without these, you are blind in unfamiliar places. Stress follows unpreparedness like a shadow.
Tell your friends and family the truth. Your response times will slow down, and that is okay. If you skip this step, they will assume you are ignoring them on purpose.
Consider setting up call forwarding for true emergencies. But then, stop checking it. The real win here is the freedom to be unreachable.
That initial itch to check your phone fades fast. What remains is actual focus and less anxiety. It is worth the awkward first week.