I do find it more challenging to deal with phone issues when out of my comfort zone, so I get your frustration.
Usually things work fine for me - either using AT&T international (in the past) or Orange esims like my past few trips. I do know that Americans are used to the (xxx) xxx-xxxx format for calling, so the slightly different format over there might make you mis-dial? But that shouldn't be an issues with "data" vs making a call, since something like Uber is a data thing.
From a data perspective, you definitely can "try" things out as soon as you have some time in Portugal (or anywhere). IOW, once you land and aren't busy, try out the Uber app BEFORE you actually need it. Open it and make sure it is behaving and knows you are in Lisbon and not in the US. Open the browser and visit a website. Maybe make a call to your room's phone. That sort of thing. If things are awry, you will at least be able to sit at the hotel, use their wifi and/or phone, and try to troubleshoot further.
In Seville a while back, I couldn't figure out how to call my tour guide to coordinate our meeting spot - we were at the "front" of the church and she wasn't there - but my wife asked a friendly local to give it a try and they dialed the number no problem :) Just my "hastiness" with not thinking it through, and a friendly local to fix it.
You might consider the broader Technology Tips section of the Travel Forum. There are lots of threads on phones and issues and the like.