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I am having trouble with the null hypothesis. In a noninferiority trial, a condition already has a standard treatment. An investigator advances the hypothesis that a new treatment is non-inferior to the standard treatment. The null hypothesis is that the new treatment is inferior by a specified amount, and the burden of proof is on the investigator to show that the new treatment is not inferior by that amount, but that the 95% confidence interval for its treatment effect excludes that prespecified size.
Here, a standard treatment is face to face therapy. The null hypothesis is that telephone interview is inferior to standard therapy with respect to the Yale-Brown checklist score. On that scale, a high score is bad and a low score is good. The null hypothesis should be that the score for standard delivery is lower than for telephone delivery. The null hypothesis as stated in the answer implies that the null hypothesis is that standard delivery is worse than telephone delivery, which is what a higher score would mean.