I remember that in the past, some teachers asked me to avoid using this sentence coz it is ambiguous.

Normally, people say it is the " you " who is at the office. But based on English grammar, ' at the office ' is about location so it has to be an ( adverbial phrase ) used to modify the verb ' call ', if that's the case, it is " I " at the office not the " you ".

Any comments ?
Yes, this sentence is terrible. It's probably only really understood in context.

I agree with "at the office" modifying "call". Afterall, the sentence "I will call you from the office" makes perfect sense -- "I" is at the office.
If ' you ' is at the office, then ' at the office ' has become either a noun phrase or an adjective phrase. But both don't look like it ???
Students: Are you brave enough to let our tutors analyse your pronunciation?
The way I see it "you" is at the office, otherwise I'll call you from the office?
 whl626's reply was promoted to an answer.
Site Hint: Check out our list of pronunciation videos.