But there would be charges If the one phone or laptop are new, right?No, the $300 limit applies to new items. Your previously used personal effects (such as laptop, phone, watch, etc.) are not included in the $300.
If you bring more than one used phone or laptop you might get some scrutiny. Some expats have posted that they have brought two laptops and told customs that one is for business and the other is for personal use and did not have a problem. Of course that could change, but having one watch, one phone, and one laptop for personal use won't result in any charges.