I'm curious to hear how common this is in the industry. Are you on-call? Was it part of your initial hire responsibilities or added later? Did you receive any compensation for your duties? Am I going to be in the same situation if I change jobs/companies?
As I progressed up the ladder I became second level support (i.e. if the 'junior guy' couldn't fix it I would get a call from them to see if I had any magic wand solutions).
As I progressed further up the ladder I began carrying three phones (one work phone, one personal phone and one for high value clients).
To this day, I have kept that third phone number active and still accept calls on it even though I am semi-retired.
I agree that being on call is disruptive and I always had trouble sleeping just in case I missed a call. I also found that not being able to drink/'smoke' etc immensely disruptive.
Being on-call on a week long rotation as an engineer with 20 years experience (as in your case) I would be like 'ah hell no, stuff it up your jumper'. Being asked to do that for zero recompense would be a hard 'No' for me but I guess it depends on your own personal circumstances in terms of being able to walk if they (employer) insisted that I either suck it up or ship out.
I’m sorry I can’t offer you any more concrete advice except my own personal experiences but hopefully others here will chime in with some more helpful input.
Best of luck.
At another company, I was the only person on call for about 4 years, no additional compensation. I controlled all the alerting, so I'd just turn down the alerts to the bare minimum. Unless the site was completely down, I didn't get paged. Everything else waited until morning. It was a B2B SaaS business and very little actively happened outside of US working hours.