Simplicity is, generally speaking, the guiding principle when selecting cell phones for seniors; flip phones, slide phones, large buttons and basic phone functions are paramount. The Nokia 100, Samsung Gusto 2, Alcatel 382G, Emporia CLICKplus V32 and the Jitterbug Plus are examples of these types of phones.
Other features worth considering when purchasing a cell phone for, or as, a senior are battery life and budget. Since seniors generally don't require the extraneous features of the app-laden smart phone, it is unnecessary to pay for a large data package. A pay-as-you-go plan, as opposed to a contract, might be the best approach.
It is also a good idea to find a cell phone with emergency and medical features programmed into them. These include medication reminders, a 911 button and an in-case-of-emergency button.