There is a very simple PHP script that interfaces with ImageMagick:
How to convert multipage TIFF to PDF in PHP
I haven't used it myself but it looks all right.
For this you will need
- ImageMagick installed
- Ghostscript installed
the linked article describes how to install those in a Ubuntu Linux environment.
Another road to take would be inserting the images directly into a auto-generated PDF file without ImageMagick. The best-known PDF generation library, FPDF, can do this, but for JPEG, PNG and GIF only.
Maybe one of these works for you.