In android contact gets backup in google account so we will use that method to transfer all the contacts of android to iPhone. Just follow the below steps to proceed .
1 In your android Goto Settings -> Accounts and sync .
2 Now there enter your gmail accounts details and click on enable synchronization.
3 Now all your contacts will get backup on your gmail account.
4 Now in your Iphone goto settings ->Mail, Contacts, Calendars .
5 Click on add accounts and then add other.
6 Now select Add CardDAV Account .
7 Fill out your account information in the following fields:
8 Server: Enter “google.com”
9 User Name: Here you will enter detail of your Google Account or Google Apps email address.
Password: Your Google Account or Google Apps password.
Description: Enter a description of the account (e.g. My contacts).
Now click on Next at top and make sure that contact option there is turned on.
Now with this when you will open contacts app all your contact will get sync from google account .