What does it mean when an elder at age 97 starts messing in their pants with diarrhea but shows no signs of illness?

I take care of a dear friend of mine whom I have known for almost 40 yrs. I have been taking care of him for 3 yrs now...as his Caregiver, Medical POA, housekeeper, cook, chauffeur, and accountant. When we connected again after many years of not seeing each other, it was as though we had never parted company. We are very close (friends) and never had a relationship other than friendship. Within the last 6 months, he has stopped being able to take care of himself regarding his personal hygiene. That's OK because I have enlisted the help of one of his male friends whom he has known and loved for many years to come over every 2 weeks to help him with his showering.
He has a heart valve problem (systemic murmur) and gets winded easily but other than that he has no major issues other than Dimentia. Lately though, he has had diarrhea a lot and is messing himself, clothing and the bathroom. Is this a sign of some sort of failure? How long should I wait before calling his physician? (who is useless by the way) Maybe it's just a phase but it concerns me.
Does anyone have some advice? Thank you all and many Blessings to all of you wonderful people!