Is it safe for someone with gerds to take cleocin (clindamycin phosphate) for a tooth. Infection?

Yes. Cleocin (clindamycin phosphate) or Clindamycin is a good antibiotic for dental infections, a strong killer of bacteria. It will have no direct effect on your gerd. It has no drug interactions. However, you can have some abdominal discomfort and even vomiting reaction to antibiotics. Get the infection under control, then have tooth treated promptly. Drink full glass of water when taking medication.
Usually. But without knowing the specifics of your case i would recommend you check with you md or whoever is treating your gerd symptoms first.