POST request to backend

How can I send data from dhtmlxGrid to php backend?

There are few possible ways

a) dataProcessor - data sent not as part of form but as separate AJAX requests, server side script ( PHP in you case ) must process incoming response and send back results of operation
    PHP based sample of dataprocessor included in pro package of dhtmlxgrid … _form.html

c) grid data can be serialized back to XML, and such XML can be sent|processed in any necessary way