hello igal.kroyter,
you may check $ gst-inspect-1.0 v4l2src, the output capabilities shows that for video/x-raw it supports YUY2, YVYU, and UYVY.
since your pixel format types as pixel_phase = "yuyv"; , you should configure the format as YUV2 in the gst pipeline.
BTW, please see-also similar forum threads for reference, Topic 288808.