Problems with my broadband connection and a cordless phone.?

My broadband connection only works reliably when my cordless phone is switched on. With the phone on its cradle and off, the DSL light on my Dynalink router, flicks on and off. My P.C.'s network diagnostics indicate that I have no connection. If I turn on the phone (Panasonic KX-144) but don't dial the DSL light stays on and I have ADSL. I have an ADSL splitter on the router and a filter on the cordless phone line.