Right now I am using the / for words and the` key for phrases. I like the / key, because I don't have to stretch my baby finger to use it. I am not as happy with using the` key for phrases, but it is okay for now.
I am avoiding the spacebar, because it is what I have used for the normal purposes for the spacebar and to use it for Instant Text seems to me interferring with the normal use of the spacebar. This may not be true, but I feel better having totally different keys for adding words and phrases in Instant Text.