The reaction is known as the Stille Coupling.
The overall reaction involves a "Pd"-catalyzed "C-C" bond formation between an organostannane and a halide or a pseudohalide.
"R"^1"-X" + "R"^2"-SnR"_3 stackrelcolor(blue)( "Pd"("PPh"_3)_4color(white)(m))(→) "R"^1"-R"^2 + "R"_3"Sn-X"
The "R"^1 and "R"^2 groups are normally sp^2 hybridized, and "X = Cl, Br, I, OTf, OSO"_2"CF"_3, or "OPO(OR)"_2.
With your starting materials, the reaction would be
underbrace(("CH"_3)_2"C=CH-Br")_color(red)("1-bromo-2-methylpropene") + "Ph-SnMe"_3 stackrelcolor(blue)( "Pd"("PPh"_3)_4color(white)(m))(→) underbrace(("CH"_3)_2"C=CH-Ph")_color(red)("2-methyl-1-phenylpropene") + "Me"_3"SnBr"
