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"#
