That could work, Sain!  She is incredibly secretive and she tends to do her jobs on her own, keeping to herself.   She tells half-truths and redirects conversations constantly.   It's quite possible that Phel heard Yula saying things like that and distrusts Yula.  For that matter,  (if you wanted to),  she could've heard Yula speaking to herself and saying strange things in that manner to further the distrust.