I don't understand your question. What role did they play in what exactly? I could be able to help you if I knew what you were referring to.
A good starting point would be describing the Phoenicians. Saying who they were, when they rose and when they fell, etc. Then end the paragraph with "This is how this magnificent culture influenced Rome" then start your essay on how they influenced it with "The first way the Phoenicians influenced Rome is..."
Hope this helped. Have a great day!
Mars and mercury is right :)
