Arm makes a specification and standard (the ARM ISA).
Apple licenses that and develops their own chip, which is then manufactured by TSMC.
So I guess if Intel dies the US will still have a few good CPU design firms, but no manufacturing
Also note that Foxconn (China) assembles the iPhones
Eg https://www.businessinsider.com/apple-iphone-factory-foxconn...
ARM also produces core reference implementations. Most ARM licensees’ licenses only allow them to use those in a slightly modified form.
What you’re talking about is an ARM IP license, which allow the company to build their own implementation of the standard. Only a few companies have those and, of those, even fewer actually use it. Apple is one of those that does.