Photographs from the scene show a line of forensic tents in the back garden, while officers have been seen going in and out of the terraced house with photographic equipment.
Plastic sheeting has also been placed from the rear of the property to the tenting.
The current owners of the property are not connected to this enquiry and have been rehoused while police search the house and garden.
Phillip left his home in St Eleanors Close, West Bromwich, on the morning of July 28 1999 to visit a friend in Northfield. Later that day he phoned his foster parents to say that he would be staying overnight with a friend.
Despite of media appeals both in Birmingham, and Manchester, where he had family links, he was never seen again.
Detective Inspector Jim Church, from force CID, said: "Sadly, there has been no proof of life for Phillip in all these years and we need to explore all the information we have to see if we can find out what happened to him.
"We have been in touch with Phillip’s family and made them aware of our investigations.
"Even though it is almost 23 years ago, we are sure that someone holds the key to Phillip’s disappearance and we would urge anyone with information to contact us."
Phillip’s family said: "We think about Phillip every day.
"We love him and miss him more than words can say.
"If anyone has any information about what has happened to Phillip or where he might be please let the police know.
"Even though he has been missing for many years we are still desperate to know where Phillip is so that we can have some closure."
Information can be given via Live Chat at west-midlands.police.uk or by contacting Crimestoppers anonymously on 0800 555 111 quoting log 1825 of 18/3.