What is the difference between colloquial an oral in the phrases, colloquial English and oral English?
Alternatively, for the linguists out there: oral refers communication medium whereas colloquial refers to register.
Considered this way, the concepts are not mutually exclusive: would you consider a speech (i.e., oral communication) given by Queen Elizabeth II colloquial? Surely not! Given by President Barack Obama? Quite possibly…
For another example: colloquial is in opposition to formal (among others), whereas oral is in opposition to written, signed, etc.
"oral English" is any spoken English. "colloquial English" is informal, and may include language that might be unacceptable for printing.
Colloquial comes from the word conversation, specifically, according to the OED
1. Of or pertaining to colloquy; conversational.
Perhaps a better way to phrase your question is - What is the difference between oral and conversational English.
Conversational English is typically oral, but oral English is not necessarily conversational.