So, you are fortunate to have a beautiful, long- hair coated Papillon or Phalene.
Sometimes you may give him a raw hide bone, and he gets his chest hair tangled in the bone.
His drool also from chewing the bone gets in his chest hair, and he starts "chewing" on the hair.
Eventually, if you let him do that too frequently, the hair breaks off.
Keep the chest hair brushed/combed daily, and apply a little spritz (water and a drop of hair conditioner) before the brushing.
Bath him once/per week to keep hair clean and soft/silky.