Tap on the 3 lined button in the top of the screen to show the left side panel and then tap on "Images".
Select multiple photos by tapping on them and then tap on "Print" button in the top right.
Tap on "Printer Options in the Print screen to choose the Image size and Paper tray.

You can choose different options using the "Printer Options" button on the Print screen.

To print multiple photos per page, tap on the "Printer Options" in the print screen. Change the "Pages per sheet - columns" and also "Pages per sheet - rows" to set the number of images per page.

Images can be printed using different sizes using the "Printer Options".

You can choose the paper tray if you are printing from your iPhone/iPad via the free WePrint on your Mac or PC https://esz.nz/wp. Paper tray selection will depend on your System and printer support.

For photo printing, it is best to use "Fill page". If photos are cut off or you see white bands, you can adjust the image margins in the WePrint settings - Images tab, or the Printer Options on the iPhone/iPad Print screen
You can use negative margins in the "Printer Options" to extend the print area if needed.

If images don't appear to be the correct size, you can also adjust the "Image scaling" setting in the WePrint settings to adjust the image scale to suit your printer. This will apply to all image size formats that you select on the iPhone eg. 3x5, 4x6, except "Fill Page"