You do this in Google Phone Number Database Ads as follows: under Tools and Settings click on Measurement – Conversions, then click on edit the specific target, in the drop-down menu, choose Secondary Phone Number Database action (only observe) . Convert Google Ads conversions from primary to secondary. After that you will need to import the conversions from GA4: under Tools and Settings click on Measurement Conversions choose New conversion action , then import and choose Google Analytics 4 properties , then click continue and save , Conversions from GA4 are shown as primary conversions in Google Ads by default.
The advantage of this last option Phone Number Database is that you continue to see the same goal in Google Ads, but only the goal that you import from GA4 is included in the bid optimizations within your campaigns. In addition you Phone Number Database can see in Google Ads what the differences are between the conversions from Universal Analytics and GA4. And these differences will certainly be there, because of the different Phone Number Database measurement methods. Keep in mind that no historical data is imported from GA4. So from the moment you put the conversions from GA4 into Google.
Ads, you will see the data Phone Number Database appear and the conversions before that date will not be included in the Google Ads reports. Export reports from Universal Analytics If you want to make sure that you want to keep certain data from Universal Analytics, you can always export reports to a CSV, Excel or PDF file or to Phone Number Database Google Sheets. Then you know for sure that you can continue to see the data from Phone Number Database past years. It is just not possible to import this data back into Google Analytics 4, since this is another measurement method and the reports are therefore structured differently.