Answer:
Phosphoric acid is a better choice than hydrochloric acid as a catalyst in an experiment because it is a weaker oxidizing agent. Hydrochloric acid is also volatile and can react aggressively with many building products.
Hydrochloric acid can produce a substitution reaction instead of an elimination reaction. This is because the chloride ion (Cl-) is a strong nucleophile. The Cl- ion will react with the carbocation to form an alkyl halide instead of an alkene.