Yes, although ovulation must have occurred for fertilization to occur and the egg must be in the fallopian tubes, a woman can become pregnant in the follicular or pre-ovulatory phase.
The reason is that sperm survive for a period of about 3-5 days in the woman's reproductive tract, so pregnancy could occur from sexual intercourse days before ovulation.
However, the egg only survives for about 12-24 hours after ovulation. Therefore, a woman's most fertile days are the 3-5 days before ovulation, the day of ovulation and the day after ovulation.
However, calculating the day when the follicular phase ends and ovulation occurs can be complicated. The day of ovulation can be variable, although the length of cycles is predictable. Therefore, it is best to combine the calendar method of estimating ovulation with other methods such as increased basal body temperature, the appearance of cervical mucus or, more accurately, with ovulation tests that detect the LH hormone in urine.