Post-lar constipation, 5d no bm. Anastomosis 5cm from anal verge. Surgeon says nothing from rear. Why? Tried colace/mom/miralax. What else can I try?

Increase MiraLax (polyethylene glycol) After low anastomosis most surgeons want to avoid any stress to the anastomosis for 6 weeks or so, personally I feels it's safe after that to use a suppository or give a gentle enema if you have difficulty evacuating (evacuating problems not uncommon after lar espiecially if colonic j pouch used)... But only your surgeons knows the exact anatomy and therefore go by his/her advice.
Needs evaluation. 5 days without a bm merits an assessment by your treating surgeon.