It is the most basic of all procedures -- partial nail avulsion with phenol matrixectomy. We all have been taught to apply phenol to the nail matrix 3 times 30 seconds each. Some practitioner add an extra application to ensure no recurrent nail growth. Others have suggested that one application is all you need to cauterized the nail matrix (by observing the whitening of the nail matrix during application). How many applications of phenol do you really need?

Depending if concentration is to the m/l borders only or total nail matrix. I have been doing 3 X 30 seconds to m/l borders with 2 sticks at the same time X 3=6 sticks total the last 25 years with great success.
Total nail-2 sticks together X 3 to cover whole matrix including nail bed.

Boberg JS, Frederiksen MS, Harton FM.

American Board of Podiatric Surgery, USA.

Chemical matrixectomy using phenol is one of the most common surgical procedures for the permanent removal of toenails. The concentration of phenol solution and duration of its application have varied widely and have not been subjected to scientific study. The authors studied the histologic effects of phenol on the nail matrix and determined the optimal concentration of phenol and time the phenol solution needs to be in contact with the nail bed.

PMID: 12438504 [PubMed - indexed for MEDLINE]