You would use the symbol for a caret (dots 4, 26) to represent the print caret showing insertion. If you have a phrase, you would enclose the phrase in base grouping indicators (dots 126 for opening and dots 345 for closing). The base grouping indicators will likely need grade 1 indicators in front of them. This use must be explained in a transcriber's note somewhere and the symbols must be on the Special Symbols page (or in a tn at the site).
Cindi