Trim
To me the phugoid is similar to a natural tendency for the a/c to roll. The cure for uncommanded roll is Dihedral. There is no similar solution for pitch linked excursions. Except for constant inputs balancing Center of lift and cg. There is no natural tendency for an aircraft to seek stable pitch in flight without a designed interruption of deviation. So many of the current crop of accidents involve Pitch, the design arena is so far inadequate to taming this most important characteristic.