Adverbs, adverbial phrases, or devices of any sort that are used to add force or emphasis to the meaning are called "intensifiers." I wonder if there is a name for phrases that caste some doubt on the accuracy of a given statement, or lessen its force. Anything that gives that effect of "take what I am saying (or what's being said) with a grain of salt"
The examples I have in mind are: "I guess", "I think," "methinketh," ect. when used at the end of a sentence.
P.S: I should add that I know the phrases "speech fillers" or "speech disfluency." They do not capture the sense I have explained above, because they usually result from too much thinking during speech, an uneasy flow of ideas, lack of confidence or lack of fluency. And this is not quite what I am looking for.