To apply one PDF sign signature to the same position on multiple pages, please select or create a sign signature firstly.
In version 10 and greator,the sign signature need to be select or created under Fill&Sign tab.
In versions prior to V10,the PDF sign signature need to be selelcted or created under PDF Sign tab and the PDF Sign tab doesn't always show up in Foxit PhantomPDF, it only appears after you click on Protect tab>PDF Sign
After you having selected a PDF sign signautre,please move the cursor to the position you want to sign and single click to place the selected signature there, then right-click on the newly added signature, choose Place on Multiple Pages…. Option in pop-up context menu, specify the page range in Place on Multiple Pages window ,click on OK.