If you don’t escape the double quotes in your statement then you will get the same error. Try the below line in AWS CLI and it should work.
aws dynamodb put-item --table-name PhoneBook --item "{""PhoneNo"":{""S"",""12345""},""Name"":{""S"",""abc""}}" --return-consumed-capacity TOTAL
This would be the output:
{
"ConsumedCapacity": {
"TableName": "PhoneBook",
"CapacityUnits": 1.0
}
}