I have a basic lead sheet that begins with an instrumental intro depicted with slashes (slash regions) and the first verse comes in as spoken not sung so there are no notes. So if I understand this, you can’t add lyrics to slashes so I would have to use a text frame in order to add the spoken lyrics?
Is a text frame in fact the correct solution in this scenario?
You can have lyrics under slashes but you need to manually place them using the caret, as they have no rhythmic values to attach to. Shift-Alt/Opt-Space gives non-breaking spaces so you can type entire sentences in the lyrics if desired.
That said, maybe ‘dumb’ text is indeed the more flexible way to go here but a text frame is not the correct solution. Frames are fixed to a location on the page, rather than to a point in the music. I would recommend using staff-attached (Shift-X) text for this.
Write in a voice with the (aproximate) rhythm you envision; add the lyrics to that voice; then hide (stems & noteheads in Engrave) and suppress the notes: the lyrics should still be attached to the rhythmic positions.
Position the caret where the sunger(s) should start talking and then use SHIFT + X text to enter the phrase (using the RETURN key where multiple lines should wrap around if necessary). Repeat for each phrase.