Simplest adapter resistors to charge a phone while the phone is an OTG host
What you need is called "accessory charging device".

When making "initial connection", by default of CC pins pulls the power role as source is associated with host function, and sink is associated with device function. When a dual-role device flips it advertising from source to sink and back, the data role switches accordingly. 

There is no way to keep the data role and reverse it the sink/source role by means of resistors alone. If a device supports host mode but needs charging, the only way is to use Power Delivery communication. Both link partners must re-negotiate the power contract by exchanging "Structured VDM" messages, DR_Swap in particular. Sorry for the inconvenience :-)