If he is not fluent in the parashiyot (sections), when he is writing the tefillin (phylacteries), he should write it from a text. What are you saying? If the parashiyot are not shegurot (fluent). So he says over here, in the beginning, you know, an amateur sofer (scribe), so he is not so expert. Especially in the maleh vechaser (full and deficient spelling), some words have a vav (the letter vav), and some words don't have a vav. In the text, or in a written text, or somebody reads it to him, right? So that he doesn't get tired.
And if the parashiyot are shegurot in a text, but let's say he knows part of the parashiyot, you know, by heart, you can write the same text in different ways. Now, the problem with writing without a text is that you can't write everything in the text. The book says it's better to always write in the text, even if you are an expert, just in order to make no mistakes.