A couple of salient points -
eBay generally don't read or respond to board posts. And they wouldn't block your phone number as a one off anyway.
Anecdotally only about 5% of members ever visit the boards and most of those only deign to post when they have a problem. So your outreach to sellers is unlikely to hit a target.
As said, those sellers who use eBay provided addresses (either through eBay labels or connecting their preferred carrier) don't actually bother checking details like phone numbers. They automate as much as they can.
