But if you have ever watched an American medical drama they are always "phoning such and such" for the patients records. Actually there's a whole other web of complication in the US to do with insurance companies and who's on the insurance companies list of providers and who isn't.
This was true 15 to 20 years ago, but is not the case anymore. Laws were passed to set interoperability standards for medical record systems and incentivize providers to share data.
A Unified Approach to Health Data Exchange - A Report From the US DHHS
Almost all of my doctors and specialists are with one large medical group practice in my area. Last year, I needed coronary bypass surgery, which is something they don't do, so I was referred to a surgical practice in NYC, where the operation was performed. I later did cardiac rehab at another hospital system in my area. All three medical groups were able to see my medical records, test results, scan images, radiology reports, etc., from the other two groups. All three groups use the same medical records software, so I'm sure that helped as well.
Determining who is in-network with your insurance is still an issue, but much less so than before. Medical practice groups have consolidated and gotten much larger. Mine has over 200 doctors, and they're all in-network with my insurance. The same was true for the large surgical practice I went to and the hospital where I did cardiac rehab. Also, about 80 million Americans have government health coverage (Medicare or Medicaid), which is accepted by all providers, so being in- or out-of-network isn't an issue for them.