I know there are already multiple threads on this topic, as well as the fallout from eBay's current policies, but it became clear to me today exactly how you can safely provide a phone number to buyers (if you're a store holder) and I thought having a post here might be useful.
Apparently it's been available for a few months, too. 
(Apologies if this has been mentioned before and I missed it, of course)
If you go to My eBay > Account > Manage communication with buyers, twoards the end will be this:
If you edit that to say yes, you can enter a customer contact number.
Spoiler
This is a copy / paste of the info shown on the eBay info page for this feature: "From September 2017 you won’t be able to include contact information, i.e. phone numbers, email addresses or social media profiles, in item descriptions, images, eBay Stores or seller profiles.
Buyers and sellers should always use eBay messaging tools, such as My Messages or Best Offer, to communicate with each other. Sharing contact information in listings often leads to transactions being taken off eBay. This is against our policies, and limits our ability to protect you in case something goes wrong.
We know that many sellers offer telephone support as part of providing great customer service. From mid-2017, if you’re an eBay Store subscriber or list in the Motor Vehicles category, you’ll be able to indicate whether or not you’d like us to share your customer service phone number with buyers via the Ask a question link."
https://sellercentre.ebay.com.au/SR17-1/Contact-Links
Buyers and sellers should always use eBay messaging tools, such as My Messages or Best Offer, to communicate with each other. Sharing contact information in listings often leads to transactions being taken off eBay. This is against our policies, and limits our ability to protect you in case something goes wrong.
We know that many sellers offer telephone support as part of providing great customer service. From mid-2017, if you’re an eBay Store subscriber or list in the Motor Vehicles category, you’ll be able to indicate whether or not you’d like us to share your customer service phone number with buyers via the Ask a question link."
https://sellercentre.ebay.com.au/SR17-1/Contact-Links
