Why won’t my phone hold the charger in place in order for it to charge

If you already tried (to no avail) all the steps provided in the support article that led you here, it might be a hardware (battery? charging port? other internal component?) problem.

I suggest that you make an appointment (*) and have your device (along with charger and cable) inspected at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> Apple – Location Selector. After checking it out, they'll give you all the available options.

Regards

Giulio

(*) You can do it:

• Online:--> Genius Bar Reservation and Apple Support Options - Apple;
• Contacting a local Apple Store or AASP among the list provided above;
• Using the "Apple Store" app, available and downloadable from AppStore.