I know what escrow is,but how would you use escrow on paypal for bitcoin since the buyer could charge back
Since you can chargeback for 180 days with PayPal, it is not feasible to use escrow, unless the escrow is assumed to release the funds after 180 days.
That's why you'll see many unentertained/failed offers on this forum to buy BTC with PayPal. Nobody wants to use PayPal.