Your desktop is getting great bandwidth, so your Cox connectivity and DOCSIS 3.0 are fine.
Is your laptop also wired?
Is the Apple AirPort Extreme your primary router?
Although your router supports 802.11ac with perhaps MIMO, your phone only supports 1 stream. If you have a lot of wireless devices in your home (thermostats, light bulbs, weight scales, etc), each device is competing for wireless time. 3 Mbps is pretty low but it depends on how many wireless devices you have.
I also hope the update works.