Good volts and amps but phone still charging slowly
The phone restricts itself to a low-current charge if the source does not indicate that it is a dedicated power supply, by tying the data pins together with a fairly low resistance.

Technically, your phone is in the wrong for using more than 100mA without asking first, and it also exceeds the 500mA that are allowed in the USB specification. In practice, these work in almost all cases because no one implements the restrictions that tightly.

The 1.3A specified for quick charging however would be far enough above the limit that several USB host implementations would detect this as a short and shut down the port, hence the additional requirement to short out the USB data pins on the power supply side to indicate a high current capable source.