Assuming that Foo Inc. has not presented any demands as to when you have to cease control over foo.com, what you want to do is to set up a HTTP 301 redirect to

Assuming that Foo Inc. has not presented any demands as to when you have to cease control over foo.com, what you want to do is to set up a HTTP 301 redirect to your new domain phoo.com and leave it indefinitely. Human traffic will probably adapt to the new domain relatively quick, but search engines can take a while to update all instances of foo -> phoo even though 301 means "permanently moved".