Update (2022):
Links to phone numbers such as https://t.me/+1XXXXXXX will lead you to a web page the same as username links do, but you can only start chatting with the user if their privacy settings allows you.
Old answer:
It’s NOT possible to link to Telegram like this for a phone numbers so far, because every user MUST add the phone number to their contact list before they can send a message to them by phone number. This limitation is because of Telegram privacy policy and abuse prevention. In more details, if Telegram allow this type of linking, a malicious party can fetch a web page like https://t.me/+1XXXXXXX for every possible number without passing authentication. That’s most probably why Telegram doesn’t have such linking feature.
However, you can link to @username of a Telegram user if he/she has any:
https://t.me/username