You should check your iOS phone-book/dialler apps with contacts export functionalitiy.  The usual export format is vcard.  There is corresponding vcard import function in many Android contact/dialler apps.  

Some phone models are bundled with migration utility app that also include automatic phone-book import/export without any user intervention.

Hi Amy,

Thanks for posting in SOTI CENTRAL.

Please follow the recommended method to migrate the iOS devices to Andriod mentioned below:

Switching from iOS to Andriod.

However, you can also use the following workaround to export the VCF file for contacts via iCloud or trusted application.

1. Head up to iCloud.com via your computer.
2. Select the contacts that you want to export
   1. either one by one
   2. or click on the gear and use Select All
3. Click the gear again and select Export vCard. Your computer will download a VCF file containing the selected contacts. The name of the file will be explicit as for how many contacts were exported
4. Plug your Android phone to the computer, copy the VCF file to the local storage and import the contacts from the Contacts or People app.

OR

1. Download and launch the app on your iPhone.
2. When the app (“MCBackup”) asks to access your contacts, tap OK
3. Tap Backup
4. Tap email, attach the VCF file to an email and send it to your Gmail account.

5. Open up the email from your Android device, download the VCF file and import your contacts to the phone.

Also, if this post has helped you in solving your inquiry, I would request you to mark the particular comment as "is solution", so others may benefit from this information.