Numbers does not have "pages" until the user presses command-P to open the Print Setup dialogue.
Select one of the sheets that will be printed in Portrait orientation.
Press command-P to open Print Setup.
Near the bottom of the dialogue, click the radio button labelled "All Sheets"
Click on each of the Sheet names at the top of the print view to check that each page has the correct orientation.
Click Print to move to the Print dialogue.
Click the PDF button at lower left, and choose Open PDF in Preview.
In Preview:
Select the thumbnail image of the sheet that is in Landscape orientation, then click the Rotate button once to rotate that sheet 90° counterclockwise or three times to rotate that sheet 270° CCW. (you will note that "edited" has been added to the document name, and there is a note that the document has been duplicated as the original (PDF) file cannot be edited.)
Print the PDF document now open in Preview, using Portrait orientation.
Discard both PDF copies, unless you have reason for retaining them, and close Preview.
In Numbers:
Close the Print dialogue (if it is still open).
Click Done to dismiss Print Setup (if it is still open).
Regards,
Barry