Q: Syn iPhone agenda with IPad,  new Ipad items appears in iPhone ,BEW iPhone items don't appear on iPad

When I make a new agenda item on my iphone6 it don't appear in my IPad 3 agenda otherwise when I make a new agenda item on my Ipad it directly  appears also in my IPhone agenda. Otherwise around would-be be must more usefull. Is there a way to make them work realy syn or hoe can a make my IPhone the " leiding" agenda.

thanks for any suggestions