If you’re working with a demand partner who’s only specialized in mobile, then there’s no point in sending them ad request (via header bidding) for page views from Desktop. You can skip the partner and save a few milliseconds. After all, the partner wouldn’t likely to win the impression, even if it bids.
You can use SizeConfig function to create labels based on the screen size. Refer the screenshot from prebid below.
Then, you can use the labels to exclude or include the bidders in the conditional ad unit logic. For instance, the following code only calls the mobile bidder when the screen size is under 767px (or mobile phone).
labelAny: [“phone”], // this bid only applies to small screen sizes