Jerry, yes. The thing about eye strain is that it is quite a complex issue, with multiple sources of eye strain, and that a person may actually suffer from multiple causes of eye strain, which makes it harder to isolate and identify each one. You have the right idea already, I know it is hard and time consuming, but you must take the time to isolate and identify the causes of your eye strain. If you dont do it, nobody is going to do it, and the problem may never be solved.
Perhaps you can try something like, every weekend (when you are not working), every saturday or sunday, limit yourself to just one display devices e.g. first saturday, phone only. Dont view any other display devices like tablets, TVs etc on that day. It is going to be hard, but it has to be done. Then see if you get eye strain or not from your phone. If your phone causes you eye strain, then you may need to find another phone. There is not much we can do if a phone causes eye strain. Same for tablet. I cannot use LG tablets at all, I get very severe eye strain within 2 minutes of using. Some tablets are not so bad i..e mild eye strain. I have my 4-year old ipad mini which i get zero eye strain, and that is the one and only tablet that I am still using until today. I do not even dare to upgrade the OS, for fear the new OS might cause eye strain. If it aint broke, dont fix it. At least I have one tablet model that I can use with zero eye strain. There might be one that you can use with zero eye strain as well, but the search for it will take time and lots of testing/trial and error. Good luck.