Although this is a phone number for Microsoft, this number cannot be used to contact Microsoft for direct assistance. Microsoft only allows callers to reach them after going through their website, meaning they must first either go onto Microsoft.com and request a call directly or talk with the online web bot and request phone assistance that way.
When you dial this number, it tells you exactly that. It does not offer a way for you to connect to anyone on the phone; it simply tells you that you must first contact Microsoft by going to its website. It provides an option to receive the website link on your phone; it will ask you if you would like the system to send you a text message with a link on how to contact Microsoft.
Once you confirm acceptance of the link, the system sends a quick text with that information. It then thanks you for calling Microsoft and automatically hangs up. You don't have anything else that you can do while you're on the phone with them.
In essence, this number is merely a way to provide contact information for people who don't have the ability or wherewithal to look up how to contact Microsoft for help. The company doesn't want to shut out people who have a hard time getting online, but that's also not the main consumer who would be calling with an Xbox-related problem anyway.
Given how much of the Xbox and its gaming are now online, this format is most likely used to allow consumers who are tied up with their gaming to get assistance without having to exit out of their games. With most games now putting a drain on available internet speeds, it's understandable that Xbox would want another way for customers to contact them without using their home internet connection to get assistance.
Overall, I understand the need to make assistance a web-first thing. Xbox makes clear that one of the reasons they're doing this is because it cuts down on wait times, which is something that can be appreciated. Most people who would take the time to call probably don't have a lot of time available before they need to get back to their games, and interrupting a game because of a call to Xbox wouldn't work if there was a long hold time.
However, this number is a starting point and nothing more. Obviously, I would not recommend it for assistance unless you're at the very beginning of your search.