Hey there! I completely understand your concerns about privacy and would be happy to help you find a FOSS alternative to Truecaller that will work on your iPhone. One option you might consider is OpenCNAM, which is an open-source caller ID system that can be used for incoming calls. You could also check out the Privacy Pro app, which blocks spam calls and messages while respecting user privacy.

Another option is DuckDuckGo's mobile browser, which includes a feature called "Privacy Protection," allowing it to block trackers and other malicious scripts from running in the background.

I hope these suggestions help you find what you're looking for! Let me know if there's anything else I can assist with.