Adding extra power to USB power lines
As Chris Stratton commented above, &quot;a properly designed phone won't pull more than the USB power limit when connected to an active USB port.&quot; The point here is that it is the phone/device that determines how much power it can sink, and for what purpose. Simple beefing up of power wires or having more capable power supply cannnot possible solve this problem.
To maintain (or charge) the phone's battery while operating in data transfer mode, the phone must be designed to do so, and it can do it only if the host port also has corresponding capabilities.
With newer USB connection standard as Type-C connector with Power Deliver function, the solution to the question is possible, but again, both link partners must have corresponding matching capabilities designed in.
The USB-C with PD works in the following way. After the cable makes an interconnect, DC voltages on CC lines are used to determine primary ports functionality. In the case of smartphone, it will likely advertise itself as &quot;device/sink&quot;, while the host port might have dual-role in terms of power - it can be a standard host source, or as a power sink (to be able to charge itself if this is a laptop).
After the direction of connection (for power) is determined after few CC-Rp-Rd cycles, the link partners exchange &quot;capability&quot; messages over the PD serial communication over the same CC lines. This communication provides both host and device with what they want and what they can do in terms of power, and &quot;power contract&quot; gets negotiated. Then there is a round of negotiations that takes place about the DATA role of the ports, and about supprt of any other alternative modes (display port, audio, debug, etc). Only after that the link partners begin USB-level communication, in negotiated direction.
All this functionality must have internal support and is controlled over several internal communnication links between CPU, Embedded Controller (EC), and PD/CC chips (and other possible data muxes). All this control is embedded in various BIOS functions and firmware patches for EC. So this is not something a DYI person can do, these functions must be designed and qualified/validated by device/host manufacturers.