Hi I have an update to my initial reply
Back Story (skip this if you just want to know how it is done) :
Today a work colleague of mine had this exact same problem and had used the Apple App "Move to IOS" on Google Play store to do it BUT ended up with the a problem - he wanted to be able to modify his contacts on his computer (he found this way faster and easier) since he had made some groups on his android phone which didn't transfer correctly(he had access to all of his contacts yes , but he wanted to be able to arrange and modify some), but after the whole Transfer experience he was unable to access or sync his contacts via iCloud (which would be the solution)
so here's what i found
What was happening (again the solution is below skip this if that what you're looking for):
After transferring, his contacts were being read straight off his Gmail account and not actually on his phone or iCloud
- you can find this out by going to "contacts" and in the top left there should be an option called "Groups" (if you have done a contact transfer)
Here it was syncing all contacts from his gmail account (that option was selected)
so to get to the solution would be to somehow get the contacts from his Gmail to his iCloud account
HERES HOW WE DID IT
Step 1.(On a Computer)Go to the Gmail account that has the Contacts and select ALL the contacts in the contacts tab
Step 2. click the "More" button - i found it to the left of the page
Step 3.here chose "export" , (he seemed to be running a Beta version of Gmail that didn't have the option and prompted him to go back to the older version and choose export , we did and it worked out )
Step4. Here a window will appear, with options to choose what groups of contacts you would like to export (example family , friends , everyone etc...) he chose everyone and lover down it asked what Format he wanted in , IMPORTANT you choose Vcard as this is the format understood by iCloud , done! We Exported it to the desktop
Step5. here you need to open and enter iCloud.com with your Apple ID - we did (with his ID obviously) , go to Contacts - Here you will find Nothing as in no contacts (if its your 1st iphone which it was in this case ) and in the very bottom left there will be an "options" icon (it resembles a cog - at least in this version it does) Here Choose IMPORT and select the Vcard file from your desktop AND POW all the contacts were now editable on iCloud!!!
Step 6. (so your iphone retrieves the contacts from iCloud) On iphone go to contacts , and in the top left where it says "Groups" Deselect everything and only leave Sync to iCloud (Its written something like that) selected
Step 7. go to settings - Contacts - and choose iCloud as you Preferred Service for Contacts (again the options are named something like this - his phone was configured in Spanish im literally translating off the top of my head ) -
-we had to do this as when he wanted to add a contact sent to him via Whatsapp App the contact was being saved automatically to his gMail account again and would not apera in his contacts list
It took a little bit of time for the contacts to sync and appear on his Iphone , it was not Instant (about 5 mins)
Hope this helps