Assume the role of a Chief Information Security Officer (CISO). Provide a detailed risk assessment of Shor's algorithm impact on RSA-2048 and Elliptic Curve Cryptography (ECC). Compare the lattice-based cryptography scheme Kyber with the hash-based signature scheme SPHINCS+. Outline a step-by-step migration plan for a financial institution to transition to post-quantum cryptographic standards, ensuring backward compatibility during the transition phase.