Since my needle tip broke, the stiching is loose on the underside. I have replaced the needle, rethreaded it several times, put a new bobbin in and it still has loose threading on the underside. I have cleaned out the bobbin area as well. I have a Phaff 1471. Any more suggestions?

Loose stitches on underside is a sign that the top thread is not under enough tension. So you need to check that the tension dial is set to correct setting (usually 4 or 5) and that the top thread is actually in the tension discs. Always thread up with the pressure foot raised to ensure the tension discs are wide open so the thread seats in fully.

So unthread top and rethread checking thread goes into the tension device fully. Lower pressure foot and pull on the thread after the tension device - it should feel firm.

Also check thread is lying in the take up lever correctly.

If you can't get it threaded up and feel tension on the top thread, then something is up with the top tension device.

You could try to clean the tension device, how you do this varies with different models but if you can access the discs, then turn tension to zero and 'floss" between the metal discs with a selvage edge of a clean piece of waste cotton fabric, if gunk comes out, keep cleaning. Refer to your manual if you've never cleaned the tension device out before. Remember to reset tension back to normal setting afterwards, rethread and try again.

If after trying these things, you can not feel any tension on the top thread, then the tension device may have broken and you'll need to take it for a service.