Charles Alexander Phillips, accused of shooting an off-duty police detective to death 16 days after he pleaded guilty to other murder and assault charges, was sentenced in D.C. Superior Court yesterday to serve a minimum of 18 years in prison in connection with the first incident.

Both deaths took place in the southeast Washington apartment of Phillips' former girl firend, Carolyn Radford, 23, Assistant U.S. Attorney Martin J. Linksy said.

Last Dec. 6, Judge H. Carl Moultrie freed Phillips, 26, on personal bond, after he admitted he stabbed Napoleon Wilcox, 43, to death last May with a butcher knife and then assaulted Radford with the same weapon, Linsku said.

On Dec. 22, Phillips allegedly confronted Det. Michael K. Riley in the Radford's apartment located at 3417 Minnesota Ave. SE, police said. A struggle ensued, the detective's gun was taken and he was shot, police said.

The charges against Phillips in connection with Riley's death are pending before a Superior Court grand jury, Linsky said.

Yesterday, Judge Moultrie sentenced Phillips to the consecutive prison terms of 15 years to life for second degree murder and 40 months to 10 years for assault with a dangerous weapon in connection with the May incident involving Wilcox and Radford, Linsky said. Both penalties are the maximum prison terms for such offenses, Linsky said.