Help with japanese sentence..?

Question:

have a bit of difficulty with this sentence from a 読み物
。

英語でも, "Thank you for the other day." とか,"It was good to see you the other day." などと言えないことはないが、日本語の　”先日はども”　のような決まり文句にはなっ…

I understand most of it but I'm a little perplexed about the phrases:
決まり文句にはなっていない。
and
などと言えないことはないが

It is a little confusing.

would appreciate all the helps.
thank you guys.

Answer:

in this case, 決まり文句 describes "frequently used phrases", but I would call 先日はどうも as one of greeting phrases (or simply a 'conjunction' to start a conversation)

などと言えないことはないが
literally means "I won't deny that you can say something like that" (not deny = positive)
--> "I think that you (barely) can say ...."