I'm trying to get my website rank high for a certain search phrase and I'm now building backlinks through blog commenting.

I was wondering how essential it is to use keyword phrase as a anchor text? If I use something that is not related at all to my search phrase, would that affect negatively to the quality of the backlink?

Reason I ask this because when submitting blog comments the name field can be used as the anchor text and if it's too spammy the comment will not be approved.

for example, I'm trying to rank my blog high in google for a term 'buy this product' and i'm pretty sure If I put that as my name in blog comments the blog owner will most likely consider it as spam and not approve it even if my comment itself is not spammy..

Would YOU pass a comment from Mr "Buy Viagra Here"?

Blog comments are not a good way of getting targetted keyphrase backlinks but they do get links all the same (even if most are for Joe Blow) and they do count in your site's total for assessing overall authority etc.

Best to use article marketing for specific targetted backlinks.