**Explanation:**

**Bond angle** is the angle formed between two adjacent bonds in a molecule. The bond angle is influenced by the repulsion between the electron pairs around the central atom. The greater the repulsion, the larger the bond angle.

In this question, we need to determine which molecule has the lowest bond angle among CH4, NH3, PH3, and H2O.

1. **CH4 (Methane):** Methane has a tetrahedral molecular geometry with four hydrogen atoms surrounding the central carbon atom. Each hydrogen atom is bonded to the carbon atom by a single covalent bond. The bond angle in methane is 109.5°.

2. **NH3 (Ammonia):** Ammonia has a trigonal pyramidal molecular geometry with three hydrogen atoms and one lone pair of electrons surrounding the central nitrogen atom. The bond angle in ammonia is 107°.

3. **PH3 (Phosphine):** Phosphine has a trigonal pyramidal molecular geometry similar to ammonia, with three hydrogen atoms and one lone pair of electrons surrounding the central phosphorus atom. However, the bond angle in phosphine is larger than in ammonia. The bond angle in phosphine is approximately 93°.

4. **H2O (Water):** Water has a bent or V-shaped molecular geometry with two hydrogen atoms and two lone pairs of electrons surrounding the central oxygen atom. The bond angle in water is approximately 104.5°.

Based on the given options, we can see that the bond angle in PH3 (93°) is smaller than the bond angles in all the other options. Therefore, the correct answer is option **C) PH3**.

It is important to note that the bond angles mentioned here are approximate values and can vary slightly due to factors such as lone pair repulsion and bond length.