Also you can't freeze addresses in Core.
You can freeze specific UTXOs in Core. Coin control gives you control over the UTXOs that you can use.
I was just discussing on a similar topic with my friend and he told me that we can connect our wallet on our smartphone to use the full node on our pc.
We would be adding our transactions to the mempool ourselves. This way we won't have to rely on a third party to add our bitcoin transactions to the mempool.
Could you let me know if this possible and if yes then how can we do it ?
I use Mycelium wallet on my phone.
IIRC, Mycelium uses their own server. Certain Android wallets are SPVs which gives the user the liberty to specify their full node provided that it has a bloom filter. Else, you can go with Electrum on Android but it requires you to specifically run an Electrum server.
Actually, you can just push the transactions to mempools directly through a full node but I imagine most people aren't very interested in that.