Need to add pixels for size how di do this?

Your image may already have enough pixels but perhaps you are exporting it with a lower image size setting. What application are you using? What workflow are you following?

For reasons that I won't bore you with, I don't edit on the iPhone. However, on the computer in either Lightroom or Lightroom Classic, it is possible to right-click on an image and choose the option to Enhance and then choose the Super Resolution option that will increase the size of the image by about 4X.