Step 1: Intercept Method
At zero frequency the line gives $V_0 = -\dfrac{\phi}{e}$, which is the point B on the axis.
Step 2: Magnitude
Therefore $\phi = e \times |OB|$.
Step 3: Eliminate Options
OA is a frequency, not an energy. The slope AB equals $\dfrac{h}{e}$, not the work function. Only the product of OB and $e$ gives the work function in joules.
Final Answer:
The work function is $e$ multiplied by OB, in joules.
\[ \boxed{\text{(C) }\text{multiplication of }(OB)\text{ and }(e)\text{ in joules}} \]