WNA1300 cuts speeds over half

I assume you have a WNA3100, not WNA1300.

The WNA3100 is a 2.4 GHz, 802.11n Wi-Fi adapter. While it is rated up to 300 Mbps, this is the link speed. A lot of bits are used for things like error correction, frame synchronization, collision detection, etc. The actual data throughput is much less. A rule of thumb is to expect throughput to be no better than 50% of the link speed. Speeds are also affected by distance, congestion from other devices, signal degradation from walls and radio noise from non-Wi-Fi devices operating in the same frequency band. 

But that's not the end of it. To achieve a link speed of 300 Mbps requires the use of 40 MHz wide channels. With 2.4 GHz Wi-Fi, a 40 MHz channel can only be used if no other neighboring Wi-Fi networks are active. Otherwise, 20 MHz channels must be used. This drops the maximum link speed to 150 MHz. Couple this with the factors above and 20 Mbps to 40 Mbps is not that unusual.

You can experiment with changing Wi-Fi channels. Use Netgear's desktop Genie program, or free programs like Vistumbler, Acrylic Wi-Fi or Airport Utility to find the least congested channel.

Otherwise, you may need to invest in a dual band Wi-Fi adapter. Not only is the 5 GHz band must less commonly used, 802.11ac is only available at 5 GHz and wider channel widths are available (up to 80 Mhz on many AC routers). This translates to a whole lot more throughput. Your phone probably supports 802.11ac, which would explain why it can do 100 Mbps without any problem.