Save the voicemails from your grandparents. One day hearing their voice will be worth more than the message.

A recording keeps something that memory does not. You can hold on to what somebody said and still lose the sound of how they said it, the pace, the way they pronounced your name. The content of the message hardly matters. The voice is the thing being preserved.

Go into your phone and save the ones you still have somewhere that will survive a new device. If you can, record a short, ordinary conversation, nothing formal, just them talking about their week. There is no rush in this and no obligation; it is simply easier now than later.