Being registered as a PhD candidate in a concrete country/organisation is sufficient to be considered as a staff member, so they are eligible, even if they do not have a working contract.
Furthermore, this organisation must be in the consortium, must have
signed the MSCA-Staff Exchanges Grant Agreement, and must send their staff (i.e.,
PhD candidate) within the project duration.
On the specific issue of thesis defence pending, the PhD candidate must
still be a staff member of their sending organisation while on secondment.
‘Staff’ means there is a contractual link that gives the sending
organisation the legal means in terms of control, supervision, and instructions
to impose on the secondee compliance with the Grant Agreement obligations (e.g.
full-time work for the activities of the project, IPR, visibility of EU funds,
confidentiality, etc.).
Beneficiaries should also consider all other eligibility criteria
mentioned in the relevant and applicable Work Programme.