Ok this in response to a relevant post :~
For some phones it is possible but not available on the FP3 range in fact hardly any phones have a simple plug in to use option.
Here is a link to such a discussion and maybe Fairphone would consider the benefits of extra longevity for phones.
The following links are for those with a young heart and an old phone: Do not try any of these experiments unless you are prepared to fail, damage the phone, burn the house down and potentially set of an explosion that could decimate your environment, if you’re not doing that already.
I’m going to update this post with other links where people have succeeded in power other phones. I will make separate posts when there is some headway on what is possible for the FP3