Does changing my budget reset the learning phase?

The short answer

Large jumps can. Small, regular increases usually do not.

There is no published threshold, and the honest answer is that it depends on how far the change moves the campaign's data. The practical rule most operators use is to raise budgets in modest steps rather than doubling in one move, and to leave the target alone while doing it.

Changing budget and target ROAS at the same time is the reliable way to make a campaign unreadable for a fortnight.

More in answers, or read the full FAQ.