Technically speaking, it is not necessary to restart your cell phone regularly, such as on a daily or weekly basis.
Modern cell phones, no matter they run on Android or IOS, are pretty stable because they are built with high-quality components and software. And the software is well designed to be efficient and optimized for the hardware it runs on. Additionally, modern cell phones are rigorously tested before they are released to ensure that they are reliable enough.
However, there are still some situations under which you may need to consider getting your cell phone restarted.
Software Updates
After installing system or app updates, a restart may be required to fully implement the changes. You'd better restart your cell phone to make sure that the updates are properly applied and any new features or bug fixes are activated.
APP Glitches
If you meet with any software-related issues like apps freezing, slow performance, or even no response to touch, you probablly need to restart your phone so as to restore normal functionality.
Battery Optimization
Restarting your cell phone can help optimize battery usage. Sometimes, certain apps or processes may continue running in the background, draining the battery. Restarting will close those resource-intensive processes and improve battery life.

If you primarily use your phone for phone calls or text messages, it is generally fine to restart it once every few months. But daily or weekly restarting will not cause any harm. After all, how often to restart your cell phone is a personal preference and may depend on your specific device and usage habits.