Phone works best when you have questions that need back-and-forth — comparing destinations, discussing hotel categories, or a group's specific needs. The enquiry form is quickest for a detailed quote, since it captures everything we need in one go rather than a back-and-forth exchange. Email is best for anything you want in writing for reference, like a detailed itinerary request.
Whichever channel you use, the same travel desk team picks it up. A good rule of thumb: if you already know your dates and destination, the enquiry form gets you the fastest detailed quote. If it needs any real discussion, a phone call gets you a useful answer faster than typing it out.