Large dark moving void in the night sky over Phoenix, Arizona

My father and I were in our backyard in Phoenix, Arizona, (high population city) on a clear night and noticed above and in front of us we couldn’t see the stars in a very large area of the sky.  We noticed by the stars disappearing in front of the object and reappearing behind that it was moving.  There were no flashing lights and no sound.  We had seen blimps over Phoenix that covered sporting events and they are very loud.  Also this was much larger than any conventional craft I had ever seen,  If it was a craft.  We could not see any structure.(estimate, 400 yards long x 250 yards wide)  No one in the neighborhood said they saw it and no mention in the news.
My father a very logical man never wanted to talk about it over the years
Witness indicates that the date of the sighting is approximate.  PD