Are guaifenesin or phenylephrine stimulants?

No.

Guaifenesin belongs to the drug class of Expectorants.

https://www.drugs.com/drug-class/expectorants.html

Guaifenesin is an ingredient in cough and cold medicines that is used to help clear mucus or phlegm from your chest when you have had a cold or flu. Guaifenesin works by making your mucus thinner and easier to cough up, which helps clear chest congestion. Guaifenesin is available as an over-the-counter (OTC) medicine and also available on prescription.

https://www.drugs.com/guaifenesin.html

Phenylephrine belongs to the drug class of Decongestants, Vasopressors

https://www.drugs.com/drug-class/decongestants.html

https://www.drugs.com/drug-class/vasopressors.html

Phenylephrine is a decongestant that is used to treat stuffy nose and sinus congestion caused by the common cold, hay fever, or other allergies.

Phenylephrine may also be used for purposes not listed in this medication guide.

https://www.drugs.com/mtm/phenylephrine.html