Transfer my number from Credo

[RHWofPA]

Hi, my son & I use Credo.  My phone number was mine from when I used Tracfone.  My son received his number from Credo.  Does that make a difference, and are both numbers transferable?  
I am still using my 6s iPhone, and my son has the 11 iPhone.  Is my phone too old to switch?  What would be a comparable phone for this old woman of 56?  

thanks so much!