PTEXT phrase = SegCreateIndirect( SegAppend( SegCreateFromText( "Hello" )
                                           , SegCreateFromText( "World" ) ) );

The resulting phrase is a single segment with no prior or next, but its content is "HelloWorld" if it was passed to buildline... it's go the content of the two text segments linked together, but not in its buffer. It is actually a 0 length buffer for a TEXT segment.