Comment by jeroenhd

There is a great youtube video I was once linked (that I sadly lost the link to since) that was a recording of an international phone call between the American, Australian, British, and Indian office, and a few non-native English speaker's offices. Each of them spoke English but the native speakers had a hard time understanding at least one or two other people on the call.

"English" is just too broad a term. Indian English is different from American English in pronunciation, preferred synonyms and even grammar. In fact, the way small grammatical features can tell the difference between "white" American English and African American Vernacular English causes some Americans to code switch to "white". Even "American English" isn't a single kind of English. Of course, you won't hear anyone but the most racist people openly complain about someone speaking AAVE but the unintentional bias towards preferring people speaking in their own accents is real and in some cases very problematic.

I think most Americans want the person on the phone to speak American English (or their preferred flavour of North American Spanish, depending on their native tongue), preferably in an accent close to theirs. That's the language, culture, and subset of dialects that they understand. It's not just Americans, of course, it's people in general; we humans like it when things are easy for us, and the less we need to pay attention to decipher what the others are saying, the better.