This is kind of a niche scenario, but when you Google making a variable from another variable php, most of the examples involve using a double dollar sign, which may not be what you want to do.
Yes, whenever possible, it makes sense to use arrays instead of weirdly-constructed variable names, but that may depend on the type of data you're working with and how it's stored in the (possibly legacy) database.
$variableaspartofname=1;
${'firstpartofname_'.$variableaspartofname.'_lastpartofname'}='whatevervalueyouwanttoassign';
That's it. If you do that, it will assign whatevervalueyouwanttoassign as the string value to a variable called $firstpartofname_1_lastpartofname.
${'firstpartofname_'.$variableaspartofname.'_lastpartofname'}='whatevervalueyouwanttoassign';